Surface treating mineral particles to reduce halide adsorption

Abstract

Mineral particles are surface treated with an alkali metal silicate, hydrogen peroxide, an acid, or an organophosphorus compound. A preferred surface treating method utilizes sodium silicate in aqueous solution at pH greater than 9, followed by neutralization with acid to precipitate a silica coating onto surface portions of the particles. The mineral particles are preferably alumina particles. The surface-treated alumina particles may be incorporated into fluoride dentifrices or compounded with halogenated hydrocarbons and polymeric resins to form flame-retardant polymer compounds.

What is claimed is: 
     
       1. A method for surface treating particles of a mineral to reduce adsorption of halide ions and halide free radicals onto surface portions of the particles, said method comprising: (a) surface treating mineral particles with an alkali metal silicate surface treating agent in an aqueous solution having an initial pH of at least 8.5;   (b) neutralizing the aqueous solution to a pH of about 5-7, thereby to precipitate a silica coating onto surface portions of the particles;   (c) separating the surface-treated mineral particles from the solution; and   (d) drying the surface-treated particles.   
     
     
       2. The method of claim 1 wherein said mineral is selected from the group consisting of alumina, bauxite, magnesia, mica, talc, hydrated calcium silicate, kaolin, hydrotalcite, calcium carbonate, magnesium carbonate, calcium phosphate, and sodium phosphate. 
     
     
       3. The method of claim 1 wherein said mineral is alumina hydrate. 
     
     
       4. The method of claim 1 wherein said solution contains about 0.3-5 wt. % sodium silicate or potassium silicate. 
     
     
       5. The method of claim 1 wherein said aqueous solution has an initial pH greater than 9. 
     
     
       6. The method of claim 1 wherein said particles have an average particle size of about 0.1-200 microns. 
     
     
       7. The method of claim 1 wherein said particles have an average particle size of about 1-30 microns. 
     
     
       8. The method of claim 1 wherein said particles are alumina trihydrate particles having average particle size of about 5-20 microns and less than about 1 m 2  /g surface area. 
     
     
       9. Alumina trihydrate particles surface-treated by the method of claim 1 and having reduced affinity for halide ions and free radicals. 
     
     
       10. Alumina trihydrate particles surface-treated by the method of claim 1, said particles having an average particle size of about 5-20 microns. 
     
     
       11. Alumina particles having an average particle size of less than about 30 microns and reduced affinity for halide ions and free radicals, said particles being surface-treated by the method of claim 1. 
     
     
       12. Alumina particles surface-treated by the method of claim 1, said particles being coated with less than about 0.2 wt. % silica. 
     
     
       13. A polymer composition comprising: (a) about 100 parts by weight of a polymeric resin;   (b) about 1-400 parts by weight alumina hydrate particles having an average particle size of about 0.1-200 microns, said particles being surface-treated by the method of claim 1, and   (c) about 5-50 parts by weight of a halogenated hydrocarbon.   
     
     
       14. The polymer composition of claim 13 wherein said resin is a thermoplastic, a thermoset, or an elastomer. 
     
     
       15. The polymer compostion of claim 13 wherein said resin is a thermoplastic selected from the group consisting of polystyrene, polypropylene, polyethylene, polyvinyl chloride, and mixtures and copolymers thereof. 
     
     
       16. The polymer composition of claim 13 wherein said resin is a thermoset selected from the group consisting of unsaturated polyesters, epoxies, polyurethanes, and mixtures thereof. 
     
     
       17. The polymer composition of claim 13 wherein said resin is an elastomer selected from the group consisting of chlorinated polyethylene, styrene butadiene rubber, natural rubber, and mixtures thereof. 
     
     
       18. A fluoride dentifrice comprising: (a) about 30-98 wt. % of a vehicle having a pH of about 5-8;   (b) about 2-70 wt. % alumina abrasive particles having an average particle size of about 1-20 microns, said particles being surface-treated by the method of claim 1; and   (c) about 0.01-2 wt. % fluoride ion dissolved in the vehicle.   
     
     
       19. In a polymer composition comprising about 100 parts by weight of a polymeric resin, about 1-400 parts by weight alumina hydrate particles having average particle size of about 0.1-200 microns and about 5-50 parts by weight of a halogenated hydrocarbon, the improvement wherein said alumina hydrate particles are surface-treated by: (a) mixing the particles with an aqueous solution of a surface treating agent selected from the group consisting of (1) an alkali metal silicate at an initial pH of at least 8.5,   (2) hydrogen peroxide,   (3) an acid selected from the group consisting of hydrochloric acid, acetic acid, phosphoric acid, phosphonic acid and phosphinic acid,   (4) an organophosphorous compound selected from the group consisting of organophosphonates having the formula RPO(OH) 2  wherein R is a C 1  C 30  hydrocarbon group, organophosphinates having the formula RR'PO(OH) wherein R is as defined above and R' is hydrogen or a C 1  -C 30  hydrocarbon group, C 1  -C 5  alkyl esters of said organophosphonates and organophosphinates, phosphoric acid monoesters having the formula ROPO(OH) 2  and phosphoric acid diesters having the formula R 2  OPO(OH);     (b) adjusting the pH of the aqueous solution to about 5-7;   (c) separating the alumina hydrate particles from the solution; and   (d) drying the surface-treated particles.   
     
     
       20. In a fluoride dentifrice comprising about 30-98 wt. % of a vehicle having a pH of about 5-8, about 2-70 wt. % alumina abrasive particles having average particle size of about 1-20 microns and about 0.01-2 wt. % fluoride ions dissolved in the vehicle, the improvement wherein said alumina particles are surface-treated by: (a) mixing the particles with an aqueous solution of a surface treating agent selected from the group consisting of (1) an alkali metal silicate at an initial pH of at least 8.5,   (2) hydrogen peroxide,   (3) an acid selected from the group consisting of hydrochloric acid, acetic acid, phosphoric acid, phosphonic acid and phosphinic acid,   (4) an organophosphorous compound selected from the group consisting of organophosphonates having the formula RPO(OH) 2  wherein R is a C 1  -C 30  hydrocarbon group, organophosphinates having the formula RR'PO(OH) wherein R is as defined above and R' is hydrogen or a C 1  -C 30  hydrocarbon group, C 1  -C 5  alkyl esters of said organophosphonates and organophosphinates, phosphoric acid monoesters having the formula ROPO(OH) 2  and phosphoric acid diesters having the formula R 2  OPO(OH);     (b) adjusting the pH of the aqueous solution to about 5-7;   (c) separating the alumina hydrate particles from the solution; and   (d) drying the surface-treated particles.